The present invention relates to brake assemblies for drawworks such as are used with oil drilling rigs and, more particularly, relates to a safety brake system for a drawworks.
Drawworks are conventionally used with an oil drilling rig or derrick to raise or lower pipe stands and drill strings into and out of the well bore. The drill string is generally attached to a hook connected to a traveling block which is secured in block and tackle fashion with a crown block secured to the top of the derrick.
The cable which runs between the traveling and crown block is securely fixed to the ground at one end so as to form a dead line. The other end of the cable is secured to a drum on the drawworks which reels the cable in and plays it out so as to raise and lower the drill string.
The drawworks includes a drive system and clutch for turning the drum and a brake system for controlling the drum as the cable is played out and to stop the drum so as to hold the drill string in a fixed position.
The brakes are ordinarily controlled by a brake lever manually actuated by the driller. Conventional brakes include a brake rim located at each end of the drum and brake bands which encircle the rims.
As drilling requirements such as deeper wells and faster speeds of drilling operations have increased, it has become harder to manually apply the band brakes to handle the greatly increased loads.
Additionally, the requirements which are placed upon the band brakes in emergency situations has also increased. Larger loads have increased the possibility of runaway operations. If a drill string is not properly slowed and stopped as it is lowered, the traveling block can strike the drilling floor and severly damage the equipment and endanger the workers.
Accordingly, there is a need for a brake system which can handle the increased loads and which can provide an emergency braking system of sufficient capacity to stop the rotation of the drum on the drawworks in emergency situations. Such a brake system is disclosed and claimed herein.